In the related art, a plurality of electronic devices performing various types of processing are mounted in a vehicle. For controlling an operation of these electronic devices, a plurality of ECUs are mounted in a vehicle. Further, in order for the plurality of ECUs to be operated in cooperation with one another, each ECU is connected with each other via a network and the plurality of ECUs share information through the transmission and reception of data. In this case, as communication protocols, a controller area network (CAN) (see ISO 11898-1: 2003 Road vehicles—Controller area network (CAN)—Part1: Data link layer and physical signaling, ISO 11519-1: 1994 Road vehicles—Low-speed serial data communication—Part1: General and definitions) has been widely adopted.
In the CAN protocol, the plurality of ECUs are connected with a bus formed of a twisted pair cable that transmits operating signals and each ECU transmits and receives digital data represented by the operating signals. Further, the CAN is a protocol of serial communication and only one ECU of the plurality of ECUs that are connected with the CAN bus can transmit data and other ECUs are controlled to stand by until one ECU ends the transmission of data. In addition, when the plurality of ECUs transmit data simultaneously, the plurality of ECUs perform an arbitration based on IDs allocated to the data and are controlled so as to transmit data having high priority.